This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
The combustion of fuel within a combustor, e.g., a combustor integrated with a gas turbine, is conventionally controlled by monitoring the temperature of the exhaust gas. At full load, typical gas turbines adjust the amount of fuel introduced to the combustor in order to reach a desired combustion gas or exhaust gas temperature. Conventional combustion turbines control the oxidant introduced thereto using inlet guide vanes. At partial load, the amount of oxidant introduced to the combustor is reduced and the amount of fuel introduced is again controlled to reach the desired exhaust gas temperature. At partial load, the efficiency of gas turbines drops because the ability to reduce the amount of oxidant is limited by the inlet guide vanes, which are only capable of slightly reducing the flow of oxidant. Additionally, there are also potential problems with lean blow out at partial load operations.
Controlling the amount of oxidant introduced to the combustor can be desirable when an objective is to capture carbon dioxide (CO2) from the exhaust gas. Current carbon dioxide capture technology is expensive due to several reasons. One reason is due to the low pressure and low concentration of carbon dioxide in the exhaust gas. The carbon dioxide concentration, however, can be significantly increased from about 4% to greater than 10% by operating the combustion process under stoichiometric or substantially stoichiometric conditions and recycling at least a portion of the exhaust gas to the combustor as a diluent in order to adjust the temperature of the exhaust gas. Also, in oxy-fuel combustion processes, the control of the oxidant is also critical since any unused oxygen in the exhaust gas is a contaminate in the captured carbon dioxide that restricts the type of solvents that can be utilized for the capture of carbon dioxide.
Controlling the combustion process via temperature monitoring, provides very little, if any, control over the composition of the exhaust gas and more particularly the amount of oxygen (O2) in the exhaust gas. The concentration of oxygen in the exhaust gas can fluctuate due to changes in the amount and/or composition of the fuel being combusted. Consequently, the temperature monitoring approach to controlling combustion is not desirable when the objective is to control the presence and concentrations of particular the components/compounds in the exhaust gas, for example oxygen.
The foregoing discussion of need in the art is intended to be representative rather than exhaustive. A technology addressing one or more such needs, or some other related shortcoming in the field, would benefit combustion systems and methods for controlling the composition of a combustion exhaust gas.